1. Field of the Invention
The present invention relates generally to a structure for supporting a rotary shaft, more specifically to the structure for supporting a rotary shaft that is inserted in a liquid tank through a wall thereof.
2. Description of Related Art
In some apparatus such as a rotary flat membrane separation apparatus, a rotary shaft is inserted in a tank, which holds a liquid, from outside through holes formed in opposite walls of the tank. Conventionally, bearings for supporting the rotary shaft are directly fixed in the holes in the walls. However, if the distance between the opposite walls is long in this structure, it is difficult to accurately align the axes of the bearings in the holes with each other. The structure is thus difficult to construct and maintain. Moreover, if the tank is deformed due to the weight of the liquid in the tank, the axes of the bearings are diverged, so that the rotary shaft supported by the bearings cannot smoothly rotate and the liquid can leak out through seal parts around the holes. Furthermore, the walls of the tank must be strong to support the rotary shaft with the bearings, which are directly fixed in the holes in the walls, and such the structure would increase both size and cost of the apparatus.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of the structure for supporting the rotary shaft that has a simple structure and has a high sealing quality.
In order to achieve the above-described object, the present invention is directed to rotary shaft supporting structure, comprising: a rotary shaft which is inserted to a liquid tank through a pair of openings formed in a pair of opposite walls of the liquid tank with a predetermined clearance between the rotary shaft and an edge of each of the pair of opposite walls of the liquid tank defining each of the pair of openings; a bearing member which supports the rotary shaft, the bearing member being arranged outside the liquid tank; a tubular casing which contains the bearing member; a seal part which is provided in the casing to seal the clearance between the rotary shaft and the casing; and a joint which watertightly and flexibly connects the casing to the opening in the wall of the liquid tank.
According to the present invention, the rotary shaft is inserted to the liquid tank through the holes in the walls of the liquid tank with a predetermined clearance, and is supported by the bearing member arranged outside the liquid tank. Thus, the hole and the bearing member are easily aligned, and also construction and maintenance of the structure are easy. Moreover, the seal part is provided separately from the liquid tank and is arranged in the casing; thus the alignment of the seal part is easy and simple. Further, since the bearing member and the seal part are arranged separately from the liquid tank, they are not affected by the deformation of the liquid tank. Therefore, the rotary shaft can always rotate smoothly while securing extremely high sealing quality. Furthermore, the liquid tank can have relatively low strength since the liquid tank has not to support the rotary shaft with the bearing member; thus the structure can be compact and the cost can be reduced.